1. Field of the Invention
The present invention relates to the field of telecommunications. More particularly, the present invention relates to a method and a system for CDMA-based satellite communications.
2. Description of the Related Art
Code Division Multiple Access (CDMA) is a more effective multiple access platform for terrestrial wireless networks than Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA) primarily because CDMA provides a greater frequency reuse efficiency by reusing the same frequency bands in geographically closer cells. The greater frequency reuse efficiency provided by CDMA is also an advantage for satellite communications. Nevertheless, while most conventional satellite networks are based on either FDMA or TDMA, newly proposed CDMA satellite networks are largely of bent-pipe nature, in that no baseband processing or switching occurs onboard a satellite.
System performance can be improved in terms of quality and capacity by onboard satellite processing and switching. However, unlike TDMA or FDMA approaches, a conventional CDMA approach used aboard a regenerative satellite requires that the different user signals be separated for onboard processing and switching. Coherent uplink demodulation may be used for onboard baseband processing and switching, but coherent demodulation necessitates a complex hardware implementation, i.e., carrier phase tracking is needed for each individual user signal, which is constrained on a satellite by limited available power.
What is needed is a way for providing CDMA communications in a satellite network without requiring coherent demodulation in uplink reception so that onboard satellite processing and switching can be conveniently performed.